Hybrid CZTSSe photovoltaic device

ABSTRACT

A photovoltaic device includes a first contact and a hybrid absorber layer. The hybrid absorber layer includes a chalcogenide layer and a semiconductor layer in contact with the chalcogenide layer. A buffer layer is formed on the absorber layer, and a transparent conductive contact layer is formed on the buffer layer.

BACKGROUND Technical Field

The present invention relates to photovoltaic devices, and moreparticularly to formation methods and devices using hybrid absorberlayers comprised of a chalcogenide compound, such as, Cu—Zn—Sn—S/Se(CZTSSe) and another high quality solar semiconductor material.

Description of the Related Art

Cu—In—Ga—S/Se (CIGSSe) technology provides high performance solar cellswith very high power conversion efficiency (PCE) of 20.3%. CIGSSe solarcells have a very large open circuit voltage (Voc) relative to bandgapwith no known issues of interface recombination. Unfortunately thereliance on rare elements, such as indium, for example, limits verylarge scale deployment of this technology.

Cu—Zn—Sn—S/Se (CZTSSe) is an emerging thin film solar cell technologyconsisting of all earth abundant elements. While progress has been madein the development of CZTSSe solar cells particularly usinghydrazine-based solution processing, a PCE of only 11.1% has beenachieved.

Several major limitations in CZTSSe solar cells exist as well. Forexample, a low Voc may be experienced, which is suspected to be due tohigh buffer-absorber interface recombination, high bulk defect states,existence of tail states in the bulk and possible Fermi level pinning inthe bulk or at an interface. Furthermore, CZTSSe also suffers from lowfill factor (FF) which is mostly due to low Voc and higher seriesresistance from various layers or potential barrier formation across thedevice.

SUMMARY

A photovoltaic device includes a first contact and a hybrid absorberlayer. The hybrid absorber layer includes a chalcogenide layer and asemiconductor layer in contact with the chalcogenide layer. A bufferlayer is formed on the absorber layer, and a transparent conductivecontact layer is formed on the buffer layer.

Another photovoltaic device includes a substrate, a first contact formedon the substrate, and a hybrid absorber layer. The hybrid absorber layerincludes a Cu—Zn—Sn—S(Se) (CZTSSe) layer and at least one semiconductorlayer in contact with the CZTSSe layer. A buffer layer is formed on theabsorber layer, and a transparent conductive contact layer is formed onthe buffer layer. Metal contacts are formed on the transparentconductive contact layer; the metal contacts and the transparentconductive contact layer form a front light-receiving surface.

A method for fabricating a photovoltaic device includes depositing afirst contact on a substrate; forming a hybrid absorber layer on thefirst contact, the hybrid absorber layer including a Cu—Zn—Sn—S(Se)(CZTSSe) layer and another semiconductor layer in contact with theCZTSSe layer; forming a buffer layer on the absorber layer; depositing atransparent conductive contact layer on the buffer layer; and patterningmetal contacts on the transparent conductive contact layer, the metalcontacts and the transparent conductive contact layer forming a frontlight-receiving surface.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a cross-sectional view of a photovoltaic device designated asType I in accordance with the present principles;

FIG. 2 is a cross-sectional view of a photovoltaic device designated asType II in accordance with the present principles;

FIG. 3 is a cross-sectional view of a photovoltaic device designated asType III in accordance with the present principles;

FIG. 4A is a band diagram and structure for a baseline CZTSSe deviceincluding a transparent conductive oxide (TCO), a CdS buffer layer and aCZTSSe absorber layer (with light coming from the TCO side);

FIG. 4B is a band diagram and structure for a baseline material deviceincluding a transparent conductive oxide (TCO), a CdS buffer layer and asemiconductor absorber layer (X) (e.g., CIGSSe);

FIG. 4C is a band diagram and structure for a Type I device including ahybrid CZTSSe/semiconductor (X) absorber layer in accordance with oneembodiment;

FIG. 4D is a band diagram and structure for a Type II device including ahybrid X/CZTSSe absorber layer in accordance with another embodiment;

FIG. 4E is a band diagram and structure for a Type III device includinga hybrid X/CZTSSe/X absorber layer in accordance with anotherembodiment; and

FIG. 5 is a block/flow diagram showing a method for forming aphotovoltaic device with a hybrid absorber layer in accordance withillustrative embodiments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In accordance with the present principles, a hybrid Cu₂(Zn,Sn)(S,Se)₄(CZTSSe) photovoltaic device is provided that combines the benefits ofearth-abundant constituent elements of the CZTSSe and a high performanceand high open circuit voltage of another high performance solar material(labeled “X” throughout for ease of reference). Semiconductor layer Xmay include, for example, CIGSSe or CdTe, although other semiconductormaterials may be employed. Cu—In—Ga—S,Se (hereinafter CIGSSe) solarcells yield very high performance, with world record efficiency of20.3%, although these materials are difficult to obtain and includeexpensive rare elements, such as Indium.

Hybrid CZTSSe devices may include a Type I device with a buffer/CZTSSe/Xconfiguration, a Type II device with a buffer/X/CZTSSe configuration anda Type III device with a buffer/X/CZTSSe/X configuration. Compared to abaseline CZTSSe device with a same total absorber thickness, all typesof hybrid devices provide higher power conversion efficiency. The hybridCZTSSe device provides a new way for performance-material costoptimization for large scale deployment of thin film chalcogenide solarcells.

It is to be understood that the present invention will be described interms of a given illustrative architecture having substrates andphotovoltaic stacks; however, other architectures, structures,substrates, materials and process features and steps may be variedwithin the scope of the present invention.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

A design for a photovoltaic device may be created for integrated circuitintegration or may be combined with components on a printed circuitboard. The circuit/board may be embodied in a graphical computerprogramming language, and stored in a computer storage medium (such as adisk, tape, physical hard drive, or virtual hard drive such as in astorage access network). If the designer does not fabricate chips or thephotolithographic masks used to fabricate chips or photovoltaic devices,the designer may transmit the resulting design by physical means (e.g.,by providing a copy of the storage medium storing the design) orelectronically (e.g., through the Internet) to such entities, directlyor indirectly. The stored design is then converted into the appropriateformat (e.g., GDSII) for the fabrication of photolithographic masks,which typically include multiple copies of the chip design in questionthat are to be formed on a wafer. The photolithographic masks areutilized to define areas of the wafer (and/or the layers thereon) to beetched or otherwise processed.

Methods as described herein may be used in the fabrication ofphotovoltaic devices and/or integrated circuit chips with photovoltaicdevices. The resulting devices/chips can be distributed by thefabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged devices/chips), as a bare die, or in a packagedform. In the latter case the device/chip is mounted in a single chippackage (such as a plastic carrier, with leads that are affixed to amotherboard or other higher level carrier) or in a multichip package(such as a ceramic carrier that has either or both surfaceinterconnections or buried interconnections). In any case, thedevices/chips are then integrated with other chips, discrete circuitelements, and/or other signal processing devices as part of either (a)an intermediate product, such as a motherboard, or (b) an end product.The end product can be any product that includes integrated circuitchips, ranging from toys, energy collectors, solar devices and otherapplications including computer products or devices having a display, akeyboard or other input device, and a central processor. Thephotovoltaic devices described herein are particularly useful for solarcells or panels employed to provide power to electronic devices, homes,buildings, vehicles, etc.

It should also be understood that material compounds will be describedin terms of listed elements, e.g., Cu—Zn—Sn—S(Se) (CZTSSe). The sameapplies for CIGSSe, CdS, etc. The compounds described herein may includedifferent proportions of the elements within the compound, e.g.,Cu_(2-x)Zn_(1+y)Sn(S_(1-z) Se_(z))_(4+q) wherein 0≤x≤1; 0≤y≤1; 0≤z≤1;−1≤q≤1, etc. In addition, other elements may be included in thecompound, such as, e.g., dopants, and still function in accordance withthe present principles. The compounds with additional elements will bereferred to herein as alloys.

The present embodiments may be part of a photovoltaic device or circuit,and the circuits as described herein may be part of a design for anintegrated circuit chip, a solar cell, a light sensitive device, etc.The photovoltaic device may be a large scale device on the order of feetor meters in length and/or width, or may be a small scale device for usein calculators, solar powered lights, etc.

It is also to be understood that the present invention may be employedin a tandem (multi-junction) structure. Other architectures, structures,substrate materials and process features and steps may be varied withinthe scope of the present invention. The tandem structure may include oneor more stacked cells.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present principles, as well as other variations thereof, means thata particular feature, structure, characteristic, and so forth describedin connection with the embodiment is included in at least one embodimentof the present principles. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This may be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, an illustrativephotovoltaic structure 10 is illustratively depicted in accordance withone embodiment. The photovoltaic structure 10 may be employed in solarcells, light sensors, photosensitive devices or other photovoltaicapplications. The structure 10 will be referred to hereinafter as a TypeI structure. The structure 10 includes a substrate 12. The substrate 12may include glass or other inexpensive substrate, such as metal, plasticor other material suitable for photovoltaic devices (e.g., quartz,silicon, etc.). A conductive layer 14 is formed on the substrate 12. Theconductive layer 14 may include molybdenum although other highwork-function materials may be employed (e.g., Pt, Au, etc.). The layer14 provides a metal contact.

A hybrid absorber layer 15 includes a layer 16 including a Cu—Zn—Sncontaining chalcogenide compound with a kesterite structure of theformula: Cu_(2-x)Zn_(1+y)Sn(S_(1-z)Se_(z))_(4+q) wherein 0≤x≤1; 0≤y≤1;0≤z≤1; −1≤q≤1 (hereinafter CZTSSe). In a particularly useful embodiment,the Cu—Zn—Sn-containing chalcogenide includes Cu₂ZnSn(S,Se)₄. In oneembodiment, the CZTSSe film or layer 16 has a thickness of between about0.2 to 4.0 microns and more preferably about 2 microns. Layer 16 may beformed by painting, sputtering, co-evaporation, electroplating, spincoating, slit casting, doctor blading, dip coating or other simplecoating processes. In one illustrative embodiment, layer 16 includesCZTS (or CZTS with some Se substituted for S) which provides a band gap(E_(g)) from about 1 to 1.5 eV. Although the major elements in CZTS areCu, Zn, Sn, S, Se, reference to CZTSSe or Cu—Zn—Sn containingchalcogenide material also includes compositions that optionally containGe replacing some or all of the Sn and that may also contain otherdopants, including Sb, Bi, Na, K, Li, Ca, etc.

CZTSSe has many benefits. It is low cost and environmentally harmless,being fabricated using naturally abundant materials. CZTSSe providesgood optical properties and has a band-gap energy from approximately 1to 1.5 eV, depending on the degree of substitution of S with Se, and alarge absorption coefficient in the order of 10⁴ cm⁻¹. Reducing thereliance on rare indium metal (also heavily consumed by one of thefastest growing industries—thin film displays) opens the possibility ofalmost limitless material supply.

A semiconductor layer 18 is formed on the conductive layer 14. Layer 16is formed on the semiconductor layer 18. The semiconductor layer 18 willbe referred to as material “X”, which may include semiconductor materialfrom groups IV, III-V, II-VI or I-III-VI₂. Semiconductor layer 18 mayinclude, e.g., GaAs, Cu—In—Ga—S,Se (CIGSSe), CdTe Ge, etc. Semiconductorlayer 18 and layer 16 complete the hybrid absorber layer 15.Semiconductor layer 18 may include monocrystalline, polycrystalline andeven amorphous material.

In one embodiment, CIGSSe is employed for layer 18 and has a chemicalformula of CuIn_(X)Ga_((1-x))Se₂ where the value of x can vary from 1(pure copper indium selenide) to 0 (pure copper gallium selenide).CIGSSe is a tetrahedrally bonded semiconductor, with the chalcopyritecrystal structure, and a bandgap varying continuously with x from about1.0 eV (for copper indium selenide) to about 1.7 eV (for copper galliumselenide). CIGSSe layer 18 provides high performance as open circuitvoltage (Voc) provided using this material is very high relative tobandgap (Eg) (e.g., Eg/q—Voc˜0.5 V) and no known issues of interfacerecombination. A buffer layer 20 is formed on the CIGSSe layer 18. Thebuffer layer 20 preferably includes CdS, which forms a high qualityjunction with layer 18, although other material may be employed.

The CIGSSe layer 18 may be manufactured by a vacuum-based co-evaporateor co-sputter processing of copper, gallium, and indium onto a substrateat room temperature, then annealing the resulting film with a selenidevapor to form the final CIGS structure. Other processes includeelectroplating. The Type I structure includes CZTSSe/X (CZTSSe on top ofX, where light is coming through CZTSSe before X).

In some embodiments, the X layer 18 includes a thickness of betweenabout 0.05 to about 2.0 microns and the CZTSSe layer 16 includes athickness of between about 0.2 to about 2.0 microns. Although otherthicknesses and combinations are contemplated.

A transparent conductive layer 22 is formed over the buffer layer 20.The transparent conductive layer 22 may include a transparent conductiveoxide (TCO), such as, e.g., indium tin oxide (ITO), aluminum doped zincoxide (AZO), boron doped zinc oxide (BZO) or other TCO materials. Thetransparent conductive layer 22 may include a thickness of between about100 and 300 nm.

Metal contacts 24 may be formed on the transparent conductive layer 22to further enhance the conductive properties of the transparentconductive layer 22. The metal contacts may include Ni, Al, Mo, Ag, Au,or any other suitable metal or alloy. Since the metal contacts 24 are onthe front, light receiving side of the device 10, their size should beoptimized to minimize shadowing loss and resistive loss.

Referring to FIG. 2, an illustrative photovoltaic structure 30 isillustratively depicted in accordance with another embodiment. Thephotovoltaic structure 30 may be employed in solar cells, light sensors,photosensitive devices or other photovoltaic applications. The structure30 will be referred to hereinafter as a Type II structure. The structure30 includes the substrate 12. The substrate 12 may include glass orother inexpensive substrate, such as metal, plastic or other materialsuitable for photovoltaic devices (e.g., quartz, silicon, Mo, flexiblesubstrate, etc.). The conductive layer 14 is formed on the substrate 12.The conductive layer 14 may include molybdenum although other highwork-function materials may be employed (e.g., Pt, Au, etc.). The layer14 provides a metal contact.

A hybrid absorber layer 35 includes a semiconductor layer 36 (Xmaterial) formed on a CZTSSe layer 38, which is formed of the conductivelayer 14. The structure 30 is the same as that of structure 10 of FIG. 1except that the materials of the hybrid layer 15 are switched for hybridlayer 35. The Type II structure includes X/CZTSSe (X layer is on top ofCZTSSe). In some embodiments, the CZTSSe layer 38 includes a thicknessof between about 0.1 to about 2 microns and the X layer 36 includes athickness of between about 0.05 to about 2.0 microns. Although otherthicknesses and combinations are contemplated.

Referring to FIG. 3, an illustrative photovoltaic structure 50 isillustratively depicted in accordance with another embodiment. Thephotovoltaic structure 50 may be employed in solar cells, light sensors,photosensitive devices or other photovoltaic applications. The structure50 will be referred to hereinafter as a Type III structure. Thestructure 50 includes the substrate 12. The substrate 12 may includeglass or other inexpensive substrate, such as metal, plastic or othermaterial suitable for photovoltaic devices (e.g., quartz, silicon, Mo,flexible substrate, etc.). The conductive layer 14 is formed on thesubstrate 12. The conductive layer 14 may include molybdenum althoughother high work-function materials may be employed (e.g., Pt, Au, etc.).The layer 14 provides a metal contact.

A hybrid absorber layer 45 includes a semiconductor layer 46 (Xmaterial) formed on the conductive layer 14. A CZTSSe layer 48 is formedon the semiconductor layer 46, and another semiconductor layer 46 isformed on the CZTSSe layer 48. The structure 50 sandwiches the CZTSSelayer 48 between two semiconductor layers 46. The Type III structureincludes X/CZTSSe/X (X layer is on top and bottom of CZTSSe). In someembodiments, the CZTSSe layer 48 includes a thickness of between about0.1 to about 2 microns and the X layers 46 include a thickness ofbetween about 0.05 to about 2.0 microns. Although other thicknesses andcombinations are contemplated.

Referring to FIGS. 4A-4E, simulation band diagrams are shown fordifferent structures to demonstrate the present principles. Each diagramhas axes that include energy (eV) versus position x (microns). Eachdiagram plots a conduction band (Ec), a valence band (Ev), a quasi Fermilevel for electrons (E_(F)n) and a quasi Fermi level for holes (E_(Fp)).

FIG. 4A shows a band diagram and structure for a baseline CZTSSe deviceincluding a transparent conductive oxide (TCO), a CdS buffer layer andthe CZTSSe absorber layer. FIG. 4B shows a band diagram and structurefor a baseline X layer (in this example CIGSSe) device including atransparent conductive oxide (TCO), a CdS buffer layer and the X(CIGSSe) absorber layer. FIG. 4C shows a band diagram and structure fora Type I device including a hybrid CZTSSe/X absorber layer. FIG. 4Dshows a band diagram and structure for a Type II device including ahybrid X/CZTSSe absorber layer. FIG. 4E shows a band diagram andstructure for a Type III device including a hybrid X/CZTSSe/X absorberlayer.

To illustrate the device physics of these hybrid solar cells devicesimulations were performed based on realistic device parameters for bothCIGSSe (FIG. 4A) and CZTSSe (FIG. 4B) solar cells using the wxAMPS™program. Also simulated were all three types of hybrid CZTSSe devices(FIGS. 4C, 4D and 4E). In this example, the baseline CZTSSe and X(CIGSSe) devices have efficiencies of 10.5% and 16.7% respectively,representing high performance devices that can be routinely producedfrom the respective technologies.

TABLE 1 Device performance comparison (Eff is efficiency) and t_(A) isthe absorber layer thickness. t_(A) Eff FF Voc Jsc Device (μm) % % VmA/cm² Baseline CIGSSe (FIG. 4A) 1.5 16.7 79.2 0.637 33.10 BaselineCZTSSe (FIG. 4B) 1.5 10.5 59.4 0.522 33.65 Type I: CZTSSe/X (FIG. 4C)1/0.5 12.2 65.8 0.539 34.40 Type II: X/CZTSSe (FIG. 4D) 0.5/1    13.774.1 0.610 30.20 Type III: X/CZTSSe/X 0.5/1/0.5 13.8 75.1 0.611 30.14(FIG. 4E)

Table 1 shows that all hybrid devices (Type I, II and III) have higherefficiencies than the baseline CZTSSe device. However, the improvementmechanisms are notably different. To illustrate the benefits and workingprinciple of these hybrid devices, a solar cell device simulationprogram was employed utilizing baseline CZTSSe and CIGSSe (as the “X”layer) absorber that yields a high performance CZTSSe and CIGSSe solarcell device that can be produced as shown in Table 1.

The Type I device yields higher Voc and higher Jsc. This Type I deviceeffectively forms a p-i-n solar cell structure. The Type II deviceyields significantly higher open circuit voltage than the baselineCZTSSe device as the good quality X layer (in this case CIGSSe) directlyforms the junction with the buffer layer. The Type III device istargeted to combine the beneficial characteristics of Type I and Type IIdevices and thus yield very high Voc, and the highest efficiency amongall these three types of hybrid devices (slightly better than Type II).

The Type I hybrid cell yields the best Jsc that surpasses even thebaseline devices. The device effectively works as a p-i-n devicestructure with the CZTSSe layer serving as the intrinsic layer and the Xlayer serving as the p-type layer. The buffer layer (CdS) serves as then-type layer. The Jsc improvement stems from the near intrinsiccharacter of the CZTSSe layer. A large potential difference between pand n introduces a wide region with large electric field thatfacilitates carrier drift and increases carrier collection and thushigher Jsc. Unfortunately, a thicker intrinsic-like CZTSSe layerincreases the series resistance that degrades the FF. Thus, thethickness needs to be optimized.

In the Type II hybrid cell, the improvement is mainly in the Voc as thehigh quality X layer (e.g. CIGSSe) becomes the junction partner with thebuffer (e.g., CdS). A high performance CIGSSe device has a very high Vocrelative to bandgap (Eg/q—Voc˜0.5 V) and no known issues of interfacerecombination with a CdS buffer.

In the Type III hybrid cell, the characteristics are almost identical tothe Type II device with a slight improvement due to the addition of theX layer at the back contact (between the CZTSSe and back metal contact),which is targeted to improve the contact quality at the back and tocreate an electron mirror by having a higher conduction band near theback contact to reduce minority carrier recombination there.

There are several parameters that can be controlled to optimize thedevice performance while minimizing the material cost such as bandgap,thickness and the order of the CZTSSe and X layers. The devicestructures in accordance with the present principles offer highperformance and cost effective thin film solar cells.

Referring to FIG. 5, methods for fabricating a photovoltaic device isshown in accordance with illustrative embodiments. It should also benoted that, in some alternative implementations, the functions noted inthe blocks may occur out of the order noted in the figures. For example,two blocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

In block 202, a first contact is deposited on a substrate. The firstcontact may include Mo or similar material, and the substrate mayinclude glass or other substrate material including a flexible material(e.g., a polymer). In block 204, a hybrid absorber layer is formed onthe first contact. The hybrid absorber layer includes a Cu—Zn—Sn—S(Se)(CZTSSe) layer and at least one X layer. The hybrid absorber layer maybe formed in a single process chamber or may be processed in differentprocessing chambers for each portion of the hybrid layer. The specificcomposition of each constituent layer of the hybrid layer may bedetermined to optimize the characteristics of the layer in accordancewith the conditions and response needed in a given application.

The CZTSSe may include Cu_(2-x)Zn_(1+y)Sn(S_(1-z) Se_(z))_(4+q) wherein0≤x≤1; 0≤y≤1; 0≤z≤1; −1≤q≤1, and the X layer(s) may include CIGSSe(e.g., CuIn_(x)Ga_((1-x))Se₂ where the value of x can vary from 1 to 0).

In block 206, performance is optimized by controlling the compositionsof the hybrid absorber layer to control at least one of thickness andband gap during the formation of the hybrid absorber layer and itslayers. In block 207, a placement order of the CZTSSe layer and the Xlayer is selected. In one embodiment, the CZTSSe layer is on top of theX layer. In another embodiment, the X layer is on top of the CZTSSelayer. The hybrid layer may also include X/CZTSSe/X. In the X/CZTSSe/Xstructure, the X layers may include the same or different semiconductormaterials.

In block 208, a buffer layer is formed on the absorber layer. The bufferlayer may include CdS although other materials may be employed, such as,e.g., CdTe, ZnS, Zn(O,S), In₂S₃, ZnO, etc. In block 210, a transparentconductive contact layer is deposited on the buffer layer. In block 212,metal contacts are patterned on the transparent conductive contactlayer. The metal contacts and the transparent conductive contact layerpreferably form a front light-receiving surface. The metal contacts arealso preferably minimized to provide maximum light absorption. In block214, processing may continue to complete the device.

Having described preferred embodiments for a hybrid CZTSSe photovoltaicdevice (which are intended to be illustrative and not limiting), it isnoted that modifications and variations can be made by persons skilledin the art in light of the above teachings. It is therefore to beunderstood that changes may be made in the particular embodimentsdisclosed which are within the scope of the invention as outlined by theappended claims. Having thus described aspects of the invention, withthe details and particularity required by the patent laws, what isclaimed and desired protected by Letters Patent is set forth in theappended claims.

What is claimed is:
 1. A photovoltaic device, comprising: a hybridabsorber layer in electrical communication and in direct contact with ametal back contact, the hybrid absorber layer comprising: aCu—Zn—Sn—S(Se) (CZTSSe) layer with kesterite crystal structure, whereinthe Cu—Zn—Sn—S(Se) (CZTSSe) layer is intrinsic, wherein a degree ofsubstitution of sulfur (S) with selenium (Se) provides for a band gapenergy for the Cu—Zn—Sn—S(Se) (CZTSSe) layer ranging from 1 to 1.5 eV; afirst semiconductor layer in contact with the CZTSSe layer, wherein thefirst semiconductor layer is a p-type semiconductor layer and comprisescopper indium gallium sulfide (CIGs); and a second semiconductor layerof copper indium gallium sulfide (CIGs) that is in contact with asurface of the Cu—Zn—Sn—S(Se) (CZTSSe) layer that is opposite a surfaceof the Cu—Zn—Sn—S(Se) (CZTSSe) layer that the first semiconductor layeris present on, the first semiconductor layer and a cadmium sulfide layerthat is n-type providing a p-i-n device having the hybrid absorbertherebetween that is intrinsic, the second semiconductor layer providinga bandgap proximate to metal back contact that reduces minorityrecombination.
 2. The photovoltaic device of claim 1, wherein the firstsemiconductor layer, the Cu—Zn—Sn—S(Se) (CZTSSe) layer, and the secondsemiconductor layer provide a p-i-n solar cell structure.
 3. Thephotovoltaic device of claim 1, wherein the second semiconductor layeris a buffer layer.
 4. The photovoltaic device of claim 3, furthercomprising a transparent conductive contact layer present on the bufferlayer.
 5. The photovoltaic device of claim 4, further comprising metalcontacts formed on the transparent conductive contact layer.
 6. Thephotovoltaic device of claim 5, wherein the metal contacts and thetransparent conductive contact layer form a front light-receivingsurface.
 7. The photovoltaic device as recited in claim 1, wherein thefirst semiconductor layer includes CuIn_(X)Ga_((1-x))Se₂ where a valueof x can vary from 1 to
 0. 8. A photovoltaic device, comprising: ahybrid absorber layer in electrical communication and in direct contactwith a metal back contact, the hybrid absorber layer comprising: aCu—Zn—Sn—S(Se) (CZTSSe) layer with kesterite crystal structure, whereinthe Cu—Zn—Sn—S(Se) (CZTSSe) layer is intrinsic, wherein a degree ofsubstitution of sulfur (S) with selenium (Se) provides for a band gapenergy for the Cu—Zn—Sn—S(Se) (CZTSSe) layer ranging from 1 to 1.5 eV; afirst semiconductor layer in contact with the CZTSSe layer, wherein thefirst semiconductor layer is a p-type semiconductor layer and comprisescopper indium gallium sulfide (CIGs); a second semiconductor layer ofcopper indium gallium sulfide (CIGs) that is in contact with a surfaceof the Cu—Zn—Sn—S(Se) (CZTSSe) layer that is opposite a surface of theCu—Zn—Sn—S(Se) (CZTSSe) layer that the first semiconductor layer ispresent on, wherein the second semiconductor layer; and a buffer layerof cadmium sulfide that is n-type present on the hybrid absorber layer,the first semiconductor layer, the hybrid absorber layer and the secondsemiconductor layer providing a p-i-n device, wherein the secondsemiconductor layer providing a bandgap proximate to the metal backcontact that reduces minority recombination.
 9. The photovoltaic deviceof claim 8, further comprising a transparent conductive contact layerpresent on the buffer layer.
 10. The photovoltaic device of claim 8,further comprising metal contacts formed on the transparent conductivecontact layer.
 11. The photovoltaic device of claim 10, wherein themetal contacts and the transparent conductive contact layer form a frontlight-receiving surface.